1. Field of the Invention
The present invention relates to a semiconductor device, a method of producing the same, and an apparatus for producing the same.
2. Description of the Related Art
With the progress in semiconductor integrated circuits in recent years, semiconductor elements having very many terminals (e.g., not less than 300 terminals) have been placed in the market. Accordingly, it has been strongly demanded to improve the technology for connecting the terminals (electrodes) of a semiconductor element to the terminals (electrodes) of a wiring board, and to reduce the cost.
Technology has been developed for connecting all the electrodes of the semiconductor element to the electrodes of the wiring substrate at one time by utilizing metal bumps. That is, metal bumps such as solder bumps or gold bumps are first attached to the electrodes of the semiconductor element, and the semiconductor element is pressed onto the wiring board, with its face directed downward, so that the metal bumps are joined to the electrodes of the wiring board and the electrodes of the semiconductor element are connected to the electrodes of the wiring board.
The conductors of the integrated circuit of a semiconductor element are formed of aluminum and, hence, the electrodes of the semiconductor elements are generally formed of aluminum. On the other hand, the conductors of a wiring board are composed of copper and, hence, the electrodes of the wiring board are generally formed of copper.
When solder bumps are to be used, a nickel layer and a titanium layer are formed on the aluminum electrodes of the semiconductor element and the solder bumps are joined to the electrodes having a composite structure of the semiconductor element, since solder joins poorly to aluminum. Thereafter, the semiconductor element is pressed onto the wiring board while being heated, so the solder bumps melt and spread on the electrodes of the wiring board, with the result that the solder bumps are surely connected to the electrodes of the wiring board.
When gold bumps are to be used, there is no need to form a nickel layer and a titanium layer on the aluminum electrodes of the semiconductor element unlike the case of using the solder bumps, since gold directly joins to aluminum. However, the gold bumps are attached to the electrodes of the semiconductor element in the form of stud bumps with projections, and, the semiconductor element is pressed onto the wiring board while being heated after the surfaces of the stud bumps are levelled, an electrically conducting adhesive is applied to the surfaces of the gold bumps, so that the gold bumps are connected to the electrodes of the wiring board via the electrically conducting adhesive. The electrically conducting adhesive comprises a mixture of a thermosetting resin and a metal filler mixed therein, and is thermally cured. Thereafter, the semiconductor element and the wiring board are sealed with a sealing adhesive (insulating resin) inserted therebetween.
When solder bumps are to be used, it is necessary to add the nickel layer and the titanium layer onto the aluminum electrodes of the semiconductor element, as described above but not all users of the semiconductor elements are necessarily allowed to apply the nickel layer and the titanium layer as desired, since application of the nickel layer and the titanium layer requires a special facility such as a vacuum chamber. Therefore, the solder bumps often cannot be used when a semiconductor element without a nickel layer and a titanium layer is purchased.
When an electrically conducting adhesive is applied to the gold bumps formed as stud bumps, on the other hand, the levelled surfaces of the stud bumps are not necessarily in parallel with the surface of the wiring circuit. Therefore, electric connection is not accomplished to a sufficient degree despite using the electrically conducting adhesive, and the reliability of connection remains low. Moreover, the materials are used in increased amounts, the steps of production are complex, and the heating must be continued until the resin is cured, hindering the productivity. Besides, in the case where the semiconductor element is defective or the mounting thereof is defective, the semiconductor element must be replaced by peeling the electrically conducting adhesive off the electrodes of the wiring board. However, it is difficult to peel it off after it is once thermally cured, since the electrically conducting adhesive contains a thermosetting resin. This makes it very difficult to repair the semiconductor element or the wiring board.
The object of the present invention is to provide a semiconductor device, and a method and an apparatus for producing the same which permit a semiconductor element to be mounted to a wiring board by a face-down technique, and to provide improved reliability of connections and simplicity of replacement of the semiconductor element.
A semiconductor device, according to the first feature of the present invention, comprises a semiconductor element having electrodes, and metal bumps including cores and metal surface layers covering said cores, said metal bumps being attached to the electrodes of said semiconductor element.
In this case, preferably, the metal surface layers comprise one of gold and solder.
Moreover, the metal surface layer is a plated layer plated on said core. The core comprises one of a metal, an inorganic material and an organic material and has a diameter of not larger than 100 xcexcm, and the metal surface layer has a thickness of not larger than 50 xcexcm. There is further provided a wiring board having electrodes, metal bumps attached to the electrodes of said semiconductor element being connected to the electrodes of the wiring board.
A semiconductor device, according to the second feature of the present invention, comprises a semiconductor element having electrodes, and metal bumps comprising gold bump elements and solder bump elements connected together, said gold bump elements being attached to the electrodes of said semiconductor element.
In this case, preferably, the gold bump element has a first side and a second side opposite to said first side, the first side of said gold bump element being joined to the electrode of the semiconductor element, and the second side of said gold bump element is joined to said solder bump element. The second side of said gold bump element forms a flat surface or a flat surface with a recessed portion. There is further provided a wiring board having electrodes, the metal bumps being attached to the electrodes of said semiconductor element are connected to the electrodes of said wiring board.
A semiconductor device, according to the third feature of the present invention, comprises a semiconductor element having electrodes, and metal bumps comprising gold-containing solder films formed on the electrodes of said semiconductor element and metal-bump elements provided on said gold-containing solder films.
In this case, preferably, there is further provided a wiring board having electrodes, the metal bumps attached to the electrodes of said semiconductor element being connected to the electrodes of said wiring board. The metal bump element comprises one of gold and solder. The metal bump element is formed as one of a metal film and a metal ball.
A method of producing a semiconductor device, according to the fourth feature of the present invention, comprises the steps of immersing a semiconductor element having electrodes in a molten gold-containing solder to form gold-containing solder films on the electrodes of said semiconductor element, and forming metal bump elements on said gold-containing solder films to thereby form metal bumps comprising said gold-containing solder films and said metal bump elements.
In this case, preferably, the step of forming the metal bump elements on said gold-containing solder films comprises immersing the gold-containing solder films in the molten solder to form solder films. The step of forming the metal bump elements on said gold-containing solder films comprises immersing the gold-containing solder films in a bath of a molten metal. The step of forming the metal bump elements on said gold-containing solder films comprises joining solid pieces onto the gold-containing solder films.
A method of producing a semiconductor device, according to the fifth feature of the present invention, comprises the steps of performing a process for imparting a fluxing action to the electrodes of the semiconductor element prior to immersing the semiconductor element having the electrodes in the molten gold-containing solder.
In this case, preferably, the process for imparting said fluxing action comprises irradiating the semiconductor element with a plasma. The step of performing the process for imparting said fluxing action comprises cleaning the electrodes of the semiconductor element with a first gas, and forming a compound of a material of the electrodes of the semiconductor element and of a second gas.
A semiconductor device, according to the sixth feature of the present invention, comprises a semiconductor element having electrodes, and metal bumps including gold bump elements having nose-like projections provided on the electrodes of said semiconductor element and solder elements formed on said gold bump elements to cover said projections.
In this case, preferably, there is further provided a wiring board having electrodes, the metal bumps attached to the electrodes of said semiconductor element being connected to the electrodes of the wiring board.
A semiconductor device, according to the seventh feature of the present invention, comprises a semiconductor element having electrodes, and metal bumps including gold bump elements provided on the electrodes of said semiconductor element and first metal layers formed around said gold bump elements to protect said gold bump elements.
In this case, preferably, the first metal layer has a melting point lower than a melting point of said gold bump element. A second metal layer is formed around said first metal layer. The second metal layer has a melting point which is lower than a melting point of said first metal layer by more than 20xc2x0 C. There is further provided a wiring board having electrodes, the metal bumps attached to the electrodes of said semiconductor element being connected to the electrodes of the wiring board.
A method of producing semiconductor devices, according to the eighth feature of the present invention, comprises the steps of attaching gold bump elements to electrodes of a semiconductor element, immersing said semiconductor element in a bath containing a molten amalgam of a mixture of a metal for protecting gold and mercury to form an amalgam layer on said gold bump elements, heating said semiconductor elements to vaporize mercury in the amalgam and to form metal films on the gold bump elements to protect gold, and transferring molten solder elements to said metal films.
A method of producing semiconductor devices, according to the ninth feature of the present invention, comprises the step of attaching gold bump elements to electrodes of a semiconductor element and transferring molten solder elements to said gold bump elements in an environment containing inert gas at an oxygen concentration of not larger than 10,000 ppm.
In this case, preferably, at least one of alcohol, ketone, ester, ether and a mixture thereof is used as a fluxing agent for transferring prior to transferring the molten solder elements. The fluxing agent for transferring comprises a flux obtained by mixing a solid component thereof in an amount of not larger than 10% by weight in an alcohol.
An apparatus for producing semiconductor devices, according to the tenth feature of the present invention, comprises a booth, a molten-solder vessel arranged in said booth so that gold bump elements provided on the electrodes of a semiconductor element can be immersed in said vessel, means for supplying inert gas into said booth, and means for detecting the oxygen concentration in said booth.
In this case, preferably, provision is further made of a flux vessel for transfer disposed in said booth. There are further provided a molten-solder vessel, arranged so that gold bump elements provided on the electrodes of a semiconductor element can be immersed in said vessel, and a support structure, for hanging said semiconductor element, said support structure including a hanging mechanism comprising at least two mutually movably coupled coupling members. The above-mentioned at least two coupling members comprises members that are coupled together like a chain.
An apparatus for producing semiconductor devices, according to the eleventh feature of the present invention, comprises a molten-solder vessel arranged so that gold bump elements provided on the electrodes of a semiconductor element can be immersed in said vessel, and a support structure for hanging said semiconductor element, said support structure including a pump-type adsorption head having an open suction hole for holding the semiconductor element.
An apparatus for producing semiconductor devices, according to the twelfth feature of the present invention, comprises a molten-solder vessel arranged so that gold bump elements provided on the electrodes of a semiconductor element can be immersed in said vessel, and a support structure for hanging said semiconductor element, said support structure including a hanging mechanism comprising at least two mutually movably coupled coupling members and a pump-type adsorption head having an open suction hole for holding the semiconductor element.